The coding scheme in G.719 has been developed and standardized for videoconferencing. According to this scheme, a frequency domain transform is performed via a modified discrete cosine transform (MDCT) to directly code an MDCT spectrum for a stationary frame and to change a time domain aliasing order for a non-stationary frame so as to consider temporal characteristics. A spectrum obtained for a non-stationary frame may be constructed in a similar form to a stationary frame by performing interleaving to construct a codec with the same framework as the stationary frame. The energy of the constructed spectrum is obtained, normalized, and quantized. In general, the energy is represented as a root mean square (RMS) value, and bits required for each band is obtained from a normalized spectrum through energy-based bit allocation, and a bitstream is generated through quantization and lossless coding based on information about the bit allocation for each band.
According to the decoding scheme in G.719, in a reverse process of the coding scheme, a normalized dequantized spectrum is generated by dequantizing energy from a bitstream, generating bit allocation information based on the dequantized energy, and dequantizing a spectrum based on the bit allocation information. When the bits is insufficient, a dequantized spectrum may not exist in a specific band. To generate noise for the specific band, a noise filling method for generating a noise codebook based on a dequantized low frequency spectrum and generating noise according to a transmitted noise level is applied.
For a band of a specific frequency or higher, a bandwidth extension scheme for generating a high frequency signal by folding a low frequency signal is applied.